This invention relates generally to the display of color images on a computer terminal and, more particularly, to a method of processing, storing, and referencing data representing image color.
In many computer terminal systems, image color data are stored as R,G,B (red, green, blue) color component values in predetermined memory locations. Often, red values are stored in one group of memory locations, green values in another, and blue values in a third group. To select a color, made up of one color value from each of the groups, the user usually specifies a color number or index. The index, which represents a single (one-dimensional) address, permits access to the particular set of RGB values representing the selected color. One such prior art "single index" system is described, for example, in U.S. Pat. No. 4,509,043 issued Apr. 2, 1985 to inventor P. X. Mossaides.
Another type of prior art system is the "true color" system, in which the true or actual colors of an object are sought to be displayed. One such true color system is described, for example, in the Model One/25 Programming Guide published Dec. 12, 1983 by Raster Technologies Corporation. In such a true color system, the user generally specifies the RGB color values themselves (rather than color numbers or indexes) to represent a selected color. The "color values" approach is representative of the true color system--a three-dimensional color referencing system. The "color number" approach is representative of the index color system--a one-dimensional color referencing system.
True color systems are generally used to produce shaded images, to display scanned-in images, and to simulate physical phenomena such as colored lights illuminating a scene composed of colored objects. Indexed color systems are generally used to depict color of icon symbols, to represent scalar values, or to distinguish image segments (e.g., primitives such as points, lines, arcs, circles, rectangles, polygons, and text).
Often it is desirable to display symbolic icons, specified in index color, superimposed on shaded images specified in true color. To accomplish this, what is needed is a system which would permit both true-color representation and index color representation.